Reproducer for sound films



Feb. 27, 1940. O, K KOLB 2,191,795

REPRODUCER FOR SOUND FILMS Filed Oct. 5, 1938 El 15 20 5 1? 13 IINVENTOR a QKJFOZZ ATTOR NEY Patented Feb. 27, 194i) UNITED I STATESPATENT jOFFlCE 2,191,795 'REPRODUCER FOR SOUND F LMs OttoKurt Kolb,Clhiswick, London, England, assignor to. British Acoustic Films Limited,London, England, a British corporation Application October 5, 1938,SerialNo. 233,383 In Great Britain January 19, 1938 7 Claims. (01.1179-1003)] w ment adapted to reproduce such films shall also be able toreproduce normal, standard or, symmetrical films. r

Normal films'require for their reproduction a substantially steady lightbeam for the purpose of energizing the necessary photosensitive devices.This, in turn, necessitates the provision of electrical and thermalmeans for producing an unvarying light source. when push-'pullfilms arebeing reproduced, it is a necessary condition that the twophotosensitive elements be accurately balanced with regard. to theirefiect on the acoustic output circuit.

' 'Heretofore it has been proposed to use suitable test films andaccurate measuring devices for the setting of the means provided foraccurately bal ancing the photoelectric effects. Such means and methodscannot, however, be employedby the operator of the equipment during theactual running of the film andthe change over from one type of film toanother.

The present invention relates to improvements in photoelectric apparatusfor the reproduction of sound films, andprovides means whereby thetesting of double photosensitive reproducing systems is facilitated andtheir exact balance and ing the actual running of the .film by simplemeans which can be easily handled by the customary operators of theprojecting and reproducing equipment.

According to the present invention circuitchanging' means areprovided toproduce pulsations of audio-frequency, e. g., of a mains frequency or ofa multiple thereof, in the light emitted by an exciter lamp. Thesepulsations may be heard in the monitoring loud speaker if there is alack of balance in the dual photosensitive system and thus serve for thepurpose of testing the balance of the dual photosensitive system.

In combination with such circuit-changing means adjustment means ofsuitable. type are provided in the circuit of each of the twophotosensitive devices, whereby their efiectsuponan output circuit underconditions of equal counter- On the other hand,-

adjustment readily obtained and maintained durphase excitation can beaccurately balanced and they can in consequence co-act upon the outputcircuit in such a manner as to produce negligible distortion in thereproduction of the light beam modulated by the film. v

More specifically, the circuit-changing means are constructed so that anexciter lamp of any known and suitable kind provided in the usual mannerfor film reproduction is fed, at the will of an operator, either byrectified and. smoothed l0 alternating current, or by unsmoothedalternating current, rectified or unrectified, and prefer- .ably ofequivalent root-mean-square value.

Figs. 1 and 2 of the accompanying drawing diagrammatically illustratetwo embodiments of the invention. v In Fig. 1 of the drawing, lightfrom. lamp lis projected by means of a condensing lens 2 upon a film 3so as to illuminate a push-pull sound record track thereon. The lightpencil passing through the film is projected by means of an objectivelens or lens system l upon a mask 5 which bears a slit lying in theplane ofthedrawing, and forms an image of the illuminated portion of thesound track thereon. The linear slit allows a flat pencil of lightcorresponding to an element of the sound track to pass through and fallupon beam-dividing optics of known kind, for example, the lenses 6 and lwhich, respectively, project divided pento oils of light upon the twophotocells 8 and 9.

The light'pencils thus falling upon the two photocells are derivedindividually from the two opposedlateral zones of the push-pull soundtrack on film 3. 3., The two cathodes of the photocells 8b and 9b areconnected to the center. tapped primary winding ID of the transformer Hwhich is provided in the usual way with an output winding 10a. connectedto a balancing potentiometer supply network. This network comprisesresistances 22, 23 and 24. Terminals of resistances 22 and 23 areconnected to common junction and in series with resistance 24. Uponresistance 24 a slid- The corresponding anodes 8a and 9a are 0 v Thelamp I is fed from transformer '2 I the output secondary 29 of which isconnected to the switch arm it which can alternatively make con-.- tacteither with a fixed contact I! or fixed contact l8, and is linkedmechanically with a switch arm 93 which makes contact with eithercontact iii or contact I6.

When the switch arms are in their upper positions and consequentlyrespectively make contacts with contacts i5 and I1, current is fed tolamp i by way of the rectifying and smoothing system 42.

When for testing purposes the switch arms are reversed in position asshown in the drawing and make contact with the fixed contacts [6 and [8,respectively, current passes through lamp I from the transformer by wayof the compensating resistance 59, which is so dimensioned or adjustedas to produce the same equivalent mean illumi nation as under theprevious conditions.

When the apparatus is in the latter position and the lamp is thus fedwith unrectified alterhating current as is well known, a ripple of twicethe supply frequency can appear in the light emitted from lamp L' If thephotoelectric efiects in the tWo .photocells 8 and 9 are not exactlycompensatory, current of twice the supply frequency will appear in theoutput circuit connected to ita and will give rise to audible hum.

This constitutes a test of the balance of the dual photoelectric system.If the hum ispresent the operator can, by adjustment of the slidingcontact 3%, bring the photoelectric system to a correct state ofbalance, which will be indicated.

by a diminution of the hum to minimum value, or under optimumconditions, by its entire disappearance. v

If any residual. hum is present, the operator can during filmreproduction reverse the switch and operate the system upon therectified and smoothed cur-rent feed.

In an alternative arrangement the resistance is may be eliminated ,andcontact 16 maybe linked by means of the conductor 32 (shown dotted) to atapping 2% on winding 30.

In a further modification illustrated in Fig. 2 there is provided arectifier 12a f ed from the transformer [29 and connected to the lamp Seither through the smoothing circuit 121), forreproduction, or throughthe compensating resistance iila, for testingby means of the switchelements i3, M in their twpalter a tiv epositions.

The invention is applicable vtoany of the lgnown n men -S n ra or elestiq l mea of which normal or push-pull films can he reproduced by dualphotosensitivedevicesand associated sound reproducing systems.

What is claimed is: v

i. In sound film, reproducing and testing apparatus, an exoiter lamp,dual photosensitive devices responsive to said lamp a source of directcurrent, 'a source of alternating current, and

circuit-changing meansfor alternatively apply-- ing to the exciter lampalternating current to test the balance of the photosensitive-devicesand direct current to operate the lamp during reproducing.

2. Apparatus according'to claim 1, in which v I the circuit changingmeans has a plurality. of

positions, a rectifying and smoothing system, a

compensating resistance, and an energizing cir- 7 cuit for said lampincluding said rectifying means in one position and'said compensatingmeans in another position of said circuit changing means. V

3. Apparatus according to claim 1 and in. which the circuit changingmeans has a plurality of positions, an energizing circuit for the.exciter lamp closed in one of said positions and including one tappingof a transformer secondary winding and a rectifying and smooth-'- nseaten and an th -en r iz n circuit i Sa d amp c os d a se ond o a dvcushions n p n n ano her t rps .Q sa d t ans? ormer s c nda y windinei.Apparatus according to claim 1, andin which said circuit changing.rneans has a plurality 0. nczs t cn a anaa eat resistan a SlFlQQPbi-llsy tem an' nereiz. n ircuit Br a xcit lam closed in one oi aidpositions. and

din the co pe satin ie is n aand a e i i ircuit o aid .eX ite lamp c osi another one of said positions and including said 1 weanling s st m- Ip 5- In p rat skior eproducin standard and Push-Pull films, a gdiu testn he, rammtien o t e la te an.

an excite? lama and controlled ;at,-.wil.1

b era r fo o era n said lamp to radiate a steadlight zbe g du n he,11enrog1uction-..of a

filmaa a nul at l h b amwdllring the test- .1

ns 9 .h e r duction .o a inushrpull film,

pna tatus accor in to laimj, and eans controlled Joy-the operator has s.y tem ca ec ediwith the iexciter lamp in n a said p sitions and a compnsati g sistance connectedwith the ,exciterflamp in anothe o sa d 7.- Aparatu Lancer it) which the means controlled Soy the ,operatorhas,

a plura it v0i LDQS EiQQa atransiormer secondary winding having twotappings, .a rectifying and sm thins s stem an ener izin cir u for a damp 1e 9 ed .91 o said n sitions and in dme e tannins an saidrectifying... and smooth.- n .1 9 1. 5am reprodu in n a en r- P g tosaid lampclosed in another .of sai positions and ;including the, secondtapping 5 r us i testin s o'rro KURTKOLBQ plain; and in photosensitiveelements;

of positions-a rectifying and smooth-f

